Conventionally, there is a device that obtains deflection angle of each rotation axis of a robot from joint torque by first obtaining joint torque applied to respective rotation axes from an attitude of the robot corresponding to a hand position command value of the robot, and by using a displacement model that shows a relationship between the joint torque and the deflection angle (refer to Patent Document 1: Japanese Patent Application Laid-Open Publication No. 4-233602).
However, in the device described in Patent Document 1, the deflection angle cannot be obtained accurately when the relationship between the joint torque and the deflection angle in the displacement model deviates from an actual relationship or when an external force acts on the rotation axis of the robot.
In addition, although it is also conceivable to detect the deflection angle with a high-performance camera or a dedicated deflection angle sensor, it is necessary to newly add a high-precision sensor or the like, and the change from the existing configuration becomes large.